Wireless communications systems rely on the behavior of radio frequency (RF) signals that propagate through space. These RF signals are commonly referred to as “carrier” signals, since information can be modulated on them and carried from the transmitter to a distant receiver over the air. In many cases, such information is modulated onto an intermediate frequency (IF) signal before being “up-converted” to the RF signal. Likewise, when RF signals are received, they are down-converted to IF. The IF signals can be more conveniently processed than the RF signals. This process of converting a received RF signal to an IF signals before down-conversion to baseband is called “superhetrodyning”. Virtually all modern radio receivers use superhetrodyning. The cost of the additional frequency conversion stage yields the benefit of better selectivity and sensitivity compared with simpler designs.
One area in which superhetrodyning is used is in receivers for receiving Link 16 signals. Link 16 is a military tactical data exchange network. Using Link 16, military aircraft, ships and ground forces can exchange information, including tactical information with very little delay from transmission to reception. Link 16 is a TDMA-based secure, jam-resistant high-speed digital data link that operates in the band of 960-1,215 MHz.